1. Field of the Invention
The present invention relates to motor vehicles and in particular to a method for controlling cylinder deactivation.
2. Description of Related Art
Methods for controlling cylinder deactivation have been previously proposed. Bolander (U.S. Pat. No. 2006/0130814) is directed to a method of regulating a displacement on demand (DOD) engine. The Bolander method teaches adjusting activation of a first cylinder to partially achieve the desired engine displacement and subsequently adjusting activation of a second cylinder to fully achieve the desired engine displacement. In other words, instead of activating multiple cylinders simultaneously, a first cylinder is activated, followed by a second cylinder being activated. During a first step before partial deactivation, the control device determines whether the displacement on demand system should be disabled. The displacement on demand system is disabled whenever the vehicle is in a situation where activation of the DOD system would be inappropriate. Such conditions include that the vehicle is in a transmission mode other than drive (i.e. park, reverse or low range). Other situations include the presence of engine controller faults, cold engine, improper voltage levels and improper fuel and/or oil pressure levels.
Foster (U.S. Pat. No. 6,904,752) is directed to an engine cylinder deactivation system that improves the performance of the exhaust emission control systems. The Foster design discloses a cylinder deactivation system to control temperature and air/fuel ratio of an exhaust gas feed-stream going into an after-treatment device. Foster teaches cylinder deactivation for controlling temperature of the exhaust gas continues as long as the operating point of the engine remains below a predetermined level, or the coolant temperature is below the operating range of 82-91 degrees C., or the exhaust gas temperature is below an optimal operating temperature of the after-treatment device, e.g. 250 degrees C. In other words, the Foster device uses a single threshold limit for the engine operating level, the coolant temperature and the exhaust gas temperature.
Donozo (U.S. Pat. No. 4,409,936) is directed to a split type internal combustion engine. In the Donozo design, the internal combustion engine comprises a first and second cylinder unit, each including at least one cylinder, a sensor means for providing a signal indicative of engine vibration and a control means for disabling the first cylinder unit when the engine load is below a predetermined value. The controller means is adapted to hold the first cylinder unit active, regardless of engine load conditions, when the engine vibration indicator signal exceeds a predetermined value indicating unstable engine operation. In the Dozono design, cylinder deactivation may occur during low load conditions any time the measured vibrations are below a particular threshold value. Dozono does not teach a method where cylinder deactivation is stopped for low load conditions based on engine speed.
Wakashiro (U.S. Pat. No. 6,943,460) is directed to a control device for a hybrid vehicle. The Wakashiro design teaches a method for determining if cylinder deactivation should be used and a separate method for determining if the engine is in a permitted cylinder deactivation operation zone. The factors used to determine if the engine is in a permitted cylinder deactivation zone are the temperature of the engine cooling water, the vehicle speed, the engine revolution rate, and the depression amount of the accelerator pedal. In each case, these factors are evaluated based on a single predetermined threshold. In other words, if each of these factors is determined to be above or below (depending on the factor) a predetermined threshold, the cylinder deactivation operation is prevented.
While the prior art makes use of several parameters in order to determine if cylinder deactivation should be stopped, there are shortcomings. The prior art teaches only threshold limits above which cylinder deactivation can continue and below which cylinder deactivation should be stopped. Also, the prior art does not teach the use of stop deactivation dependent on various parameters including engine speed, vehicle speed, transmission ratio, or engine load. There is a need in the art for a system and method that addresses these problems.